**3.1 Importation**

Importation of natural enemies, is also called as *classical biological control*. It refers to the planned introduction of an exotic biological control agent for permanent establishment and long-term pest control to an area that is invaded by pest. Its

**Figure 1.** *Three general approaches to biological control.*

#### *Biological Control of Agricultural Insect Pests DOI: http://dx.doi.org/10.5772/intechopen.104464*

target is to restore the balance between pest and natural enemy populations in the area invaded by pest without its natural enemies [1].

The import of pests either accidentally, or in some cases, intentionally in any countries where they are not native is continuous. However, due to a lack of natural enemies to suppress their populations, these introduced organisms of exotic origin may become pests, In these cases, importation of natural enemies can be highly effective [19]. Following the identification of the country of origin of the imported pest, a search may be conducted to explore a promising natural enemy. If the natural enemies are identified, their potential impact on the pest in the native country may be evaluated and imported into the new country for further study. Natural enemies are imported into the country under permit by the concerned authorities. The introduced natural enemies are first placed in quarantine for one or more generations to ensure the accidental importation of undesirable species (diseases, hyperparasitoids etc.). Further permits are required from concerned authorities for shipping to different states and field release.

The alfalfa weevil, *Hypera postica* (Gyllenhall) is a native of Europe. The species was introduced and detected in several countries. The first introduction was detected in the US in Utah in 1904. Biological control of this pest is best example of a successful program using importation of natural enemies [20].

### **3.2 Augmentation**

Manipulation of natural enemies for enhancing the effectiveness of biological control is termed as augmentation. This can be adopted by one, or both, of the two general methods as given below:

1.mass production and periodic colonization; or.

2.Genetic enhancement of natural enemies

The first one mass production and periodic colonization is most commonly used. The natural enemies are produced in insectaries, and thereafter, released either inoculatively or inundatively. Augmentation is used where populations of a natural enemy are not present or cannot respond quickly enough to the pest population. This approach, therefore, does not provide permanent solution for the suppression of pests, as the outbreak of pest may occur with importation or conservation methods.

The use of the parasitoid wasp, *Encarsia formosa* Gahan, to suppress populations of the whitefly, *Trialeurodes vaporariorum* is one of the best example of the inoculative release method [21, 22]. The whiteflies are a global pest of vegetable and floriculture crops that is very difficult to manage with pesticides. Immediate release of *E. Formosa* following detection of the first whitefly on the crop effectively prevent the populations from developing to damaging levels. The releases should be made in context of an integrated crop management program taking into account the low tolerance of the parasitoids to pesticides.

#### **3.3 Conservation**

When we are to introduce any biological control attempt, conservation of natural enemies is key element for successful effectiveness. The factors which may limit the effectiveness of natural enemy must be identified, further modifying them to enhance the effectiveness.

This approach may be adapted by two ways as follows:

1. reduce the factors which interfere with natural enemies or

2.provide the resources that natural enemies need in their environment

Several factors are responsible for reducing the effectiveness of a natural enemy. Pesticide applications may directly kill natural enemies or have indirect effects through crop reduction in the numbers or availability of hosts. Cultural practices such as tillage or burning of crop debris may be detrimental for natural enemies by killing them or reducing their population by destroying the habitat. In orchards, frequent tillage may generate dust deposits on leaves, killing small predators and parasites and further, increasing certain insect and mite pests.

A study revealing the biological control of California red scale, *Aonidiella aurantii* natural (Maskell), suggests that the control may be achieved through periodic washing of citrus tree foliage that increases the parasitoids efficiency [23]. Some host plant effects such as chemical defenses which are harmful to natural enemies but the pest on the host plant is best adapted to it, also reduces the effectiveness of biological control. There are some pests that are able to sequester toxic components of their host, and use them as defense against their own enemies. In such cases also the effectiveness of biological control is reduced. Some cases like physical characteristics of the host plant such as leaf hairiness, may reduce the ability of the natural enemy to find and attack hosts.

Therefore, conservation ensures that the ecological requirements of the natural enemy are reached out in the cropping environment. To be effective, natural enemies may need access to; alternate hosts, adult food resources, overwintering habitats, constant food supply, and appropriate microclimates [24]. In a study reported by Doutt and Nakata [25] *Anagrus epos* Girault, is the fundamental parasitoid of the grape leafhopper, *Erythroneura elegantula.* A substitute is needed in grape vineyards for overwintering. This host, another leafhopper, overwinters on blackberry foliage in riparian areas, at some distance from the vineyards. Thus, during spring season the occurrence of early colonization by the parasitoids is often observed in the vineyards near to the natural blackberry. This forms the healthier and preferable biological control. Wilson et al. [26] have reported that the French prune trees also harbor another overwintering host. Their plantation in the upwind of the vineyards will effectively conserve *A. epos*.

## **4. Current applications of biological control**

Biological control is an interesting science. This control method is constantly incorporating and introducing new knowledge and techniques. This part will deal with different ways by which efficient biological control may be adapted to meet the current pest management challenges.

#### **4.1 Modern approaches in augmentation of natural enemies**

Augmentation generally involves mass-production and periodic colonization of natural enemies. This has imparted to its commercial development. Recently, there are hundreds of commercially available biological control products for pest invertebrates, vertebrates, weeds, and plant pathogens.

The practice of augmentation not only differs for importation and conservation or in making a change in an agro ecosystem to improve its efficacy. Rather, this approach seeks to adapt natural enemies to fit into existing systems.

#### *Biological Control of Agricultural Insect Pests DOI: http://dx.doi.org/10.5772/intechopen.104464*

Inundative release of *Trichogramma* wasps is an excellent example of an augmentative practice is successfully adapted in agricultural systems. These are minute endoparasitoids Their eggs are released on the crops timed to the presence of pest eggs. *Trichogramma* is highly efficient biological control agent and most widely augmented species of natural enemy. Worldwide, over 32 million ha of agricultural crops and forests are treated annually with *Trichogramma* spp. in 19 countries, mostly in China and republics of the former Soviet Union [27].

Developed countries such as China, generally follow a simple, low labour cost, innovative technology for agricultural production and pest management systems. They highly use the *Trichogramma* spp. for the management *Chilo* spp., populations in sugarcane. The natural enemies are inundatively released and are protected from rain and predators inside emergence packets. Their eggs commercially reared in insectaries are wrapped in sections of leaves and slipped by hand over blades of sugarcane. *Trichogramma* is mostly produced in localized areas of China.

Implementation of biological control in western countries have to face socioeconomics issues for its implementation [28]. Current in large-scale production agricultural systems, some incentives are there on the efficiency and economy of scale. Large industries have developed around the application of agrichemicals, including application equipment manufacturing, distribution and sales, as well as application services. Therefore, biological control products have to compete strongly with pesticides, they should be as effective as pesticides and they should have the capacity to be applied quickly on a large scale with conventional application equipment. So it is expected that the biological agents must have many characteristics same as pesticides.

In Western country such as Europe, commercial marketing of three products utilizing the European native, *Trichogramma brassicae* Bezdenko, to suppress the European corn borer, *Ostrina nubilalis* Hübner, in corn fields was almost possible following two decades of intensive research [29]. Annual application of these products in approximately 7,000 ha, 150 ha, and 15,000 ha is carried out in Switzerland and Germany, Austria and France respectively. All the three products are manufactured in plastic or paper packets for safeguarding the wasps against weather extremes and predation until their application in the field.

*Trichogramma* products are mostly manually applied to crop fields. With the exception of Trichocaps, which may be disseminated either by hand or by aircraft using conventional application equipment. Their packets are walnut-shaped cardboard capsules (2 cm. diam.) and contain approximately 500 parasitized Mediterranean flour moth, *Ephestia kuehniella* Zwolfer, eggs [30]. Developing *Trichogramma* inside capsules are induced into an overwintering (diapause) state in the insectaries. These are then stored in refrigerated conditions for nine months without loss of quality. By this system, production of *Trichogramma* product during winter months may be possible. The product may then be distributed to growers when needed in the summer.

When the refrigerated *Trichogramma* is removed from cold storage, it will start its development inside the capsules and begin emergence approximately 100°C. It is required to control this 'reactivation' process for uniform emergence of *Trichogramma*, at different developmental stages, in the fields. The companies only make planning and preparation of the product for its application. The growers are only responsible for applying the product to crop fields.

#### **4.2 Landscape ecology and the conservation of natural enemies**

The land disturbance studies and its effects on insect community dynamics as well as the emergence of the discipline of landscape ecology have imparted the way to think about the conservation of natural enemies. Since last 20 years, ecologists have recognized the central role of disturbance in the structuring of ecological communities [21–32]. Among the various ecosystems, the terrestrial ecosystems is highly disturbed one and this ecosystem experiences one disturbance event every several years (e.g. fire in grasslands), however, in agricultural ecosystems multiple events occur in each growing season (plowing, planting, nutrient and pesticide applications, cultivation and harvest) and their outcomes may be anticipated from an ecological point of view [33]. Highly disturbed systems exhibit reduced species diversity and short food chains, resulting to well adaptation of the species (i.e. pests) which have only few natural enemies to reduce their populations. Therefore, the role of additional disturbance events, such as pesticide applications, is needed to be initiated that controls the initial negative symptom, may also precipitate its reoccurrence.

Due to increasing reliance on mechanization and pesticides, diversity in farmlands has rapidly disappeared and the impacts on natural enemies must be studied and understood [34]. Increased habitat fragmentation, isolation and decreased landscape structural complexity destabilizes the biotic interactions which serve to regulate natural ecosystems [35, 36]. Therefore, this current systems of crop production (mechanization and use of pesticides) shape the physical structure of our agricultural landscapes [37].

The goal of an ecological approach to conservation biological control is just to modify the intensity and frequency of disturbance to a point where the natural enemies can effectively function. This requires its occurrence in field, farm and larger landscape-levels. Few modifications of tillage intensity and frequency (reduced tillage or no-tillage) in fields leave behind increased plant residue on the soil surface and have a positive influence on the predators (ground beetles and spiders) as well. Similarly, intercropping may be also modified, changing the microclimate of crop fields will make them more favorable for the parasitoids [38].

When taking at the farm level, the presence and distribution of non-crop habitats can be dangerous for natural enemy survival. *Eriborus terebrans* (Gravenhorst) is a wasp which parasitizes European corn borer larvae. They grow at moderate temperatures and require a source of sugar (nectar of flowering plants or aphid honeydew). But they are unable to met these demands in a conventionally managed corn field. Therefore, wasps seek more sheltered locations in wooded fence rows and woodlots where they find reduced temperatures, higher relative humidity and abundant sources of adult food. Besides, they also parasitize European corn borer larvae in corn field edges near their habitats at two to three times the rate of those in field interiors (up to 40%) [39]. Thus, the current research is creating natural enemy resource habitats and examining the potential of modifying corn production systems to increase natural control of European corn borers. Intercrops, strip crops, as well as modification of grass waterways, shelterbelts, buffer and riparian zones are some of the promising techniques in this regard.

Now at the landscape-level, the physical structure of agricultural production systems can have an impact on the pest and natural enemy diversity and abundance. Ryszkowski et al. [34] has reported in his study in the mosaic landscapes that natural enemies are highly dependent on refuge habitats than are pests and the greater abundance of these refuges in the mosaic landscapes resulted in their higher diversity, abundance and ability to respond to prey numbers. Further studies have also revealed enhanced parasitism of true armyworm, *Pseudaletia unipuncta* (Haworth), in structurally-complex versus simple agricultural landscapes. The parasitism in the complex sites was three times higher than in the simple sites (13.1% versus 3.4%). This differences was attributed to the abundant population of one wasp species, the braconid, *Meterous communis* (Cresson) in the complex sites.

#### *Biological Control of Agricultural Insect Pests DOI: http://dx.doi.org/10.5772/intechopen.104464*

Earlier, conservation was endeavored with introduction of one species at a time, concentrating to fulfill the needs of natural enemy in a particular system. Though it is a useful approach, now it seems possible that basic ecological theory could inform the design and management of landscapes to conserve and enhance the effectiveness of entire communities of natural enemies.
